Doppler vor beacon



Sept. 13, 1966 c. w. EARP 3,273,152

DOPPLER VOR BEACON Filed May 16, 1965 Inventor CHARL ES PV. EARP Attorney United States Patent 3,273,152 DOPPLER VOR BEACON Charles William Earp, London, England, assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed May 16, 1963, Ser. No. 280,834 Claims priority, application Great Britain, May 30, 1962,

20,7 47 62 I 6 Claims. ((31. 343-108) The invention relates to Doppler VOR beacons of the type in which there is simulated a radiating source moving on a circle, and to an antenna arrangement for such beacons.

One method of achieving this simulation is by coupling each of the antennas of a circular array in turn to a transmitter. Where reference is made in this specification to a source moving this does not imply that any antenna is in physical motion but that a receiver co-operating with such a Doppler VOR beacon experiences a wave having a frequency modulation owing to the coupling of the transmitter to successive antennas.

The phase and deviation of the frequency modulation depends both on the position of the receiver relative to the beacon, to the phase of the coupling movement, and to the diameter of the circular array.

Such beacons are often used to guide an aircraft equipped with a co-operating receiver in the vicinity of an airport preparatory to its landing.

The ring of equispaced horizontal loops previously used as the antenna arrangements in Doppler VOR beacons are comparatively fragile and liable to damage by the mechanical shock. For this reason antenna arrangements of this type are unsuitable for guiding aircraft to an exact point of touchdown.

Another difficulty encountered in beacons having a ring of aerials is that the proximity of the neighbouring aerial to the aerial actually being coupled results in a distortion of the radiated field.

An aim in making the present invention is to provide an antenna arrangement for a Doppler VOR beacon which is less susceptible to mechanical shock than previous antenna arrangements for such beacons.

Another aim is to provide an antenna arrangement wherein the radiations from individual antennas are not so influenced as in previous arrangements by the proximity of the other antennas in the arrangement.

According to the invention, there is provided radio beacon equipment including a hollow metal circular cylinder having in its curved surface a row of parallel slots constituting a circular array of slot antennas, means to feed the slot antennas cyclically and consecutively around the circle with a first wave train, means to feed the antennas in a similar order with a second Wave train, the two feeding cycles being always diametrically opposite on the circle and progressing at a constant rate, and means to radiate via one or more slot antennas a third wave train midway in frequency between the first and second wave trains.

An antenna arrangement, and its operation in a beacon station is described hereafter with reference to the accompanying drawing of which:

FIG. 1 shows a pictorial view of a cylinder having a row of slots;

FIG. 2 shows a method of locating the antenna arrangement beneath a runway; and

FIG. 3 shows a section on a small portion of the antenna arrangement of FIGS. 1 and 2 and, diagrammatically, apparatus for commutating the antennas.

Referring to FIG. 1, there is shown an enclosed hollow metal cylinder 1 of right circular form having in its ICC curved surface a row of regularly spaced vertical slots 2 constituting slot antennas.

The slot antennas 2 are fed by three separate Waves in the following manner.

The waves are:

(1) A first wave of frequency F commutatively coupled to the slots 2 singly in succession, the commutation frequency being G.

(2) A second wave of frequency F similarly fed to the slots 2, the particular slot being fed by the second wave at any instant being always diametrically opposite the slot being fed by the first wave; and

(3) A third wave of frequency F midway between F and F fed continuously to all of the slots 2 in parallel, and being amplitude modulated at the same frequency, G, as that of the commutation of the first and second waves to the slots. The amplitude modulation is synchronized with the commutation cycles, so that the phase of the AM is an indication of which particular slot is being fed with the first or second wave at any instant.

The radiation pattern from a slot 2 is roughly hemispherical in form. Thus at any instant there will be received at any point within practical range of the beacon, either the first wave or the second wave, in addition to the third wave which it will be recalled is radiated from all the slots simultaneously.

The procedure at a distant receiver station for evaluating its angle of elevation from the beacon is to relate a Doppler frequency deviation or maximum shift to the deviation which would be obtained if the receiver station were at the same horizontal level as the beacon. When the receiver station is vertically above the beacon the Doppler frequency deviation is zero.

The Doppler frequency modulation arises due to the circular movement of the sources of the first and second waves simulated by the commutation cycles. The first preferred step in deriving the frequency modulation is to beat the first and second waves (which arrive separately) with the third wave in a non-linear device. Since the frequency F of the third wave lies midway between the frequencies F and F the heat wave has a constant frequency, say The beat wave has a frequency modulation of deviation equal to the Doppler deviations on the first and second waves. If at some instant the frequency of the first wave reaching the receiver is apparently (F -l-x), i.e. (Fa-i-f-i-X), the beat wave has frequency (f-l-x). At this instant, the second wave is not propagated towards the receiver due to the hemispherical direction pattern of a slot, but if the pattern were omnidirectional, the apparent frequency of the second wave would be (F -ac), i.e. (F fx), which would similarly give rise to a beat wave of instantaneous frequency (f+x). Thus the beat wave, although produced alternately by the beating of the first and the second waves with the third wave is coherent, and if there is any overlapping when the first and second waves are both received at once, the two beat waves will have the same frequency.

It is possible and desirable to arrange, at the point of overlap where the first and second waves are both received at once, that the two beat waves will have the same phase as well as frequency. This is achieved by correct phasing of the third wave with respect to the first and second waves.

There will be difficulties in maintaining this phase relationship for all angles of elevation, but it is practical for a limited range of elevation angle, say from 0 to 30 In this case the heat wave at (f-l-x) suffers no phase transient, and very little amplitude modulation.

The second preferred step at a receiver to evaluate its angle of elevation from the beacon is to apply the heat wave to a frequency discriminator, the amplitude of whose output will be an indication of the frequency deviation, i.e.

the maximum value of x, say d. From a knowledge of the frequency deviation D which would have been observed if the receiver had been on the same horizontal level as the beacon, which deviation will be a characteristic of the beacon, the angle of elevation can be calculated as sin -d/D.

The procedure for the evaluation of the horizontal bearing of the receiver from the beacon is to derive the amplitude modulation of frequency G present on the third wave, which modulation is phase-related to the commutation cycle, and to compare it in phase with the output of the frequency discriminator, which will also be a wave of frequency G.

The components in a receiver equipped to carry out this procedure are well-known, and may include preamplifiers, broad-band filters etc. or any other normal refinements. The third Wave need not be AM-detected if it is only required to measure angles of elevation.

The electronic equipment at the beacon station to produce the three waves consists of a single transmitter and a side-band generator. The third Wave then has a frequency exactly midway between those of the first and second waves.

The equipment to generate the three waves can be three independent transmitters, but the frequencies would have to be carefully controlled to maintain constant frequency separations.

FIG. 2 shows an arrangement for the physical protection of the system from impacts, hot jets of gas, etc. A well is dug in an aircraft runway 3, and the steel cylinder 1 and the necessary electrical connections, equipment, etc. are placed therein. The runway is rebuilt with asbestos or other heat-resisting nonconductive material 4, concreted over, and an aircraft may then be guided to rest over the cylinder 1.

Referring now to FIG. 3, there are shown output leads 5, 6 and 5', 6 from transmitters 7 and 7 respectively tuned to the frequencies F and F coupled through respective rotary connectors 8, 9 and 8, 9' to rotatable capacitive segments 10, 11 and 10', 1 1'. Fixed capacitive segments 12 lying in a ring are connected one to each of the metallic portions separating adjacent slot antennas (four of which can be see at 2).

A given slot antenna is energized by coupling the metallic portions each side of the slot to the two outputs of either transmitter 7 or 7'.

In operation, the four rotatable capacitive segments 10, 11 and 10', 11 are moved around in a circle so as to pass close to the fixed segments 12 in succession. In this way, the slots 2 are successively energized with the outputs of transmitters and 7 and 7.

The waves at frequency F are generated by having an energized loop aerial 13 on the axis within the cylinder 1 fed by a transmitter 14, the waves from which will propagate out of all the slots.

Alternatively the Waves at frequency F could be transmitted from a separate horizontal loop located outside the cylinder 1 but on the axis. It is obvious that transmitters 7, 7' and 14 could be replaced by a single transmitter, as hereinbefore mentioned.

It is to be understood that the following description of specific examples of this invention is not to be considered as a limitation on its. scope.

What I claim is:

1. Radio beacon equipment including, a hollow metal circular cylinder having in its curved surface a row of parallel slots constituting a circular array of slot antennas, means to feed the slot antennas cyclically and consecutively around the circle with a first wave train, means to feed the antennas in a similar order with a second wave train, the two feeding cycles being always diametrically opposite on the circle and progressing at a constant rate, and means to radiate via one or more slot antennas a third wave train midway in frequency between the first and second wave trains.

2. Equipment according to claim 1 wherein the third wave train carries a reference signal phase correlated with the feeding cycle.

3. Equipment according to claim 2 wherein the cylinder is located in a Well in the ground and covered over with a protective non-conductive material.

4. Equipment according to claim 1, wherein the successive antenna feeding means includes a capactive switch.

5. Equipment according to claim 1 wherein the third wave train is fed to all the slots by energizing a loop aerial located on the axis within the cylinder.

6. Equipment according to claim 1 wherein the first and second wave trains are derived from the third by AM sideband generation.

References Cited by the Examiner UNITED STATES PATENTS 1,898,474 2/1933 Willoughby 343- 1 2,665,381 1/1954 Smith et a1 343-770 2,760,192 8/1956 Shanklin 343-770 X 3,103,663 10/1963 Parker 343108 3,181,159 4/1965 Krarnar et a1. 343l06 CHESTER L. JUSTUS, Primary Examiner.

H. C. WAMSLEY, Assistant Examiner. 

1. RADIO BEACON EQUIPMENT INCLUDING A HOLLOW METAL CIRCULAR CYLINDER HAVING IN ITS CURVED SURFACE A ROW OF PARALLEL SLOTS CONSISTING A CIRCULAR ARRAY OF SLOTS ANTENNAS, MEANS TO FEED THE SLOTS ANTENNAS CYCLICALLY AND CONSECUTIVELY AROUND THE CIRCLE WITH A FIRST WAVE TRAIN, MEANS TO FEED THE ANTENNAS IN A SIMILAR ORDER WITH A SECOND WAVE 